In the manufacture of business forms it is generally necessary to seal the forms using adhesives. The adhesives seal the various parts of the form together in a manifold suitable, for example, for mailing. The adhesive typically is sandwiched between two portions of a form that are folded together or that overlap.
In the prior art, heat or moisture has been used to activate the adhesives that seal business forms. Heat or moisture activated adhesives are generally undesirable in many business form processes because the activating heat or moisture can damage the form, erase or smudge ink printed on the forms, such as with a non-impact laser printer, and because the apparatus needed to apply heat and moisture to the adhesive is complex and difficult to maintain. Accordingly, there has been a need to avoid conventional heat or moisture activated adhesives. Alternatively, self-activated adhesives, such as those that are tacky to the touch, have been used to seal forms. Self-activated adhesives also have disadvantages. Because self-activated adhesives are tacky, they adhere to most surfaces against which they contact. A form having a self-activated adhesive will adhere to the processing equipment or to adjacent webs and tends to cause paper jams that stop the processing equipment. Accordingly, the tackiness of self-activating adhesives is a significant disadvantage in form processing equipment.
Pressure sensitive adhesives overcome many of the disadvantages of self-activated adhesives and adhesives activated by heat or moisture. Pressure sensitive adhesives are activated by relatively large pressures, such as 100 to 200 lbs. per lineal inch of paper width. Pressure sensitive adhesives are not tacky and do not adhere to surfaces until they are activated by large pressures. A significant advantage of pressure sensitive adhesives is that they can be applied to web stock used in the manufacture of business forms without any concern that these adhesives will prematurely adhere to adjacent web material or to equipment surfaces. Webs coated with strips of pressure sensitive adhesives can be stacked; transported in hot, cold and damp conditions; fed through forms handling equipment, such as rollers, impact printers and non-impact printers; perforated and cut without activating the adhesive. Pressure sensitive adhesives are only activated when subjected to a relatively large pressure that is substantially greater than any pressure that the web coated adhesive will normally experience. Accordingly, the activation of a pressure sensitive adhesive can be controlled to occur at the appropriate time and place in the form manufacture process by application of sufficient pressure to activate the adhesive.
Pressure sensitive adhesives have been used in business forms. Conventional pressure sealing apparatus for sealing multilayered business forms usually apply pressure to the entire web to activate the pressure sensitive adhesive strips on the form. Since the pressure required to activate the pressure sensitive adhesive is typically about 200 lbs. per lineal inch of paper width, a tremendous amount of force must be applied by these conventional devices to generate a pressure sufficient to activate the adhesive. Moreover, to ensure that the force applied by these conventional machines is uniformly distributed over the web area, the mechanical devices that apply the pressures to the webs must be extraordinarily rigid and have a smooth, uniform surface that contacts the web. In addition, the web surfaces must also be clean and smooth, so that the force applied by the mechanical devices is evenly distributed over the entire web and all portions of the web are subjected to the adhesive activating pressure. If the machine or web is not smooth and clean, then there may be portions of pressure sensitive adhesive on the web that are not subjected to pressure sufficient to activate the adhesive. If there is insufficient pressure, then portions of the adhesive will not be activated and will not adhere to the business form.
To overcome shortcomings in conventional pressure sealing devices, a class of devices has been developed which have been uniquely designed to apply adhesive-activating pressures to only those portions of a form in the vicinity of pressure activated adhesives. Several examples of these devices are described in the above-identified applications. These devices employ a variety of mechanisms, such as rollers, pinching rollers, slotted rollers, conveyor webs, and other devices, to selectively apply great pressure to predetermined portions of a business form. The claimed invention is a further improvement in this class of pressure sealing devices that selectively apply pressure to business forms to activate pressure activated adhesives.